Several aspects of the Kdp system, an ATP-driven K ion transport system of Escherichia coli K-12, will be studied. We are pursuing studies of an unusual regulatory mechanism in which changes in turgor pressure control the expression of the Kdp system. The regulator protein for this system, the product of the kdpD gene, will be characterized, and strains in which this protein is overproduced will be sought. When available, these will be used for in vitro studies of kdp gene expression. Other work will complete our biochemical characterization of the system, including the structure of the phosphorylated intermediate, further kinetic analysis of the intermediate, and completion of structural studies to determine which region of which of the three proteins making up the Kdp system are exposed on which side of the membrane. Restriction analysis of the kdp genes is progressing. Selected fragments are being cloned into an amplifiable plasmid so that higher levels of the proteins for biochemical studies can be obtained, and DNA sequence analysis of regions of interest can be done.